全文获取类型
收费全文 | 335篇 |
免费 | 31篇 |
专业分类
366篇 |
出版年
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2017年 | 7篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 10篇 |
2013年 | 15篇 |
2012年 | 15篇 |
2011年 | 15篇 |
2010年 | 13篇 |
2009年 | 5篇 |
2008年 | 10篇 |
2007年 | 12篇 |
2006年 | 6篇 |
2005年 | 5篇 |
2004年 | 18篇 |
2003年 | 10篇 |
2002年 | 15篇 |
2001年 | 14篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 11篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1965年 | 4篇 |
1954年 | 2篇 |
1928年 | 2篇 |
1926年 | 2篇 |
1925年 | 2篇 |
1923年 | 6篇 |
排序方式: 共有366条查询结果,搜索用时 15 毫秒
101.
Gregory?R.?JacobsEmail author Eric?L.?Bruestle Anna?Hussey Dimitry?Gorsky Aaron?T.?Fisk 《Biological invasions》2017,19(5):1533-1546
Species invasions can alter food web structure and change ecosystem-level functioning, but it is often unclear how these invasions may affect the life history of native species. The Lake Sturgeon (Acipenser fulvescens), a large long-lived native fish species in the Great Lakes, has increased in abundance in the lower Niagara River and nearby Lake Ontario during a period of invasive species-induced ecosystem change precipitated most recently by Dreissenid mussels (Driessena polymorpha and Driessena bugensis) and Round Goby (Neogobius melanostomus). Material taken from cross-sections of archived pectoral spines from Niagara River Lake Sturgeon captured in 1998–2000 and 2010–2012 were analyzed for stable isotopes across discrete growth zones to provide an ontogenetic assessment of diet, and diet analysis of Lake Sturgeon captured in 2014 was conducted to assess the contribution of invasive prey. Round Goby was the most important Lake Sturgeon prey item (86% by weight) in 2014, which corroborated results of δ15N and δ13C. Lake Sturgeon captured after the invasion of Round Goby exhibited ontogenetic changes in δ15N that differed from pre-Round Goby patterns, though this effect was weaker for δ13C. Values of δ15N from spine growth zones indicated non-linear increases in trophic position with age and increased rate of δ15N enrichment after the Round Goby invasion. We conclude that Round Goby establishment in western Lake Ontario changed the feeding ecology of Lake Sturgeon, which may have a positive effect on population growth for this native species. 相似文献
102.
103.
Growing cotton in a greenhouse with 12-h of supplemental light [8,608 lux (800 ft-c) from combination of mercury and Lucalux® lamps] resulted in 2 × to > 3 × greater reproduction of Meloidogyne incognita and Belonolaimus longicaudatus as compared to natural light alone. Rate of increase of Hoplolaimus galeatus was affected little in this experiment. In a second experiment under controlled conditions in a phytotron, light source and intensity had greater influence on the reproduction of Heterodera glycines and Pratylenchus penetrans on soybean than on B. longicaudatus. Fluorescent plus incandescent and metal halide light sources resulted in the greatest nematode reproduction. Lucalux lamps resulted in much lower rates of nematode increase than other light sources. Rates of nematode increase on soybean under the different light sources in the phytotron generally were positively related to plant growth. 相似文献
104.
Methylation-sensitive single-strand conformation analysis (MS-SSCA) is a method of screening for methylation changes at CpG sites in a region of DNA. After bisulfite modification, the region of interest is amplified using primers specific for bisulfite-modified sequences. The amplified products are denatured and run on a nondenaturing polyacrylamide gel. The sequence differences caused by methylation lead to the formation of different secondary structures (conformers) with different mobilities. MS-SSCA is a convenient and rapid method for screening large numbers of samples for methylation. Individual bands can readily be isolated and sequenced allowing more detailed analysis of methylation changes. In this article, we present a protocol for MS-SSCA and outline strategies for the design of primers for amplifying bisulfite-modified DNA sequences. 相似文献
105.
Deeks MJ Cvrcková F Machesky LM Mikitová V Ketelaar T Zársky V Davies B Hussey PJ 《The New phytologist》2005,168(3):529-540
The closely related proteins AtFH4 and AtFH8 represent the group Ie clade of Arabidopsis formin homologues. The subcellular localization of these proteins and their ability to affect the actin cytoskeleton were examined. AtFH4 protein activity was identified using fluorimetric techniques. Interactions between Arabidopsis profilin isoforms and AtFH4 were assayed in vitro and in vivo using pull-down assays and yeast-2-hybrid. The subcellular localization of group Ie formins was observed with indirect immunofluorescence (AtFH4) and an ethanol-inducible green fluorescent protein (GFP) fusion construct (AtFH8). AtFH4 protein affected actin dynamics in vitro, and yeast-2-hybrid assays suggested isoform-specific interactions with the actin-binding protein profilin in vivo. Indirect immunofluorescence showed that AtFH4 localized specifically to the cell membrane at borders between adjoining cells. Expression of an AtFH8 fusion protein resulted in GFP localization to cell membrane zones, similar to AtFH4. Furthermore, aberrant expression of AtFH8 resulted in the inhibition of root hair elongation. Taken together, these data suggest that the group Ie formins act with profilin to regulate actin polymerization at specific sites associated with the cell membrane. 相似文献
106.
Pediatric-based Helicobacter?pylori research continues to contribute significantly to our understanding of both clinical and pathophysiological aspects of this infection. Here, we review the published pediatric H.?pylori literature from April 2009-March 2010. Analysis of pediatric H.?pylori strains continues to suggest that cagA(+) and cagPAI competent strains are less prevalent than in adult isolates. Studies from the Middle East report a high H.?pylori prevalence and intrafamilial transmission. Data continue to show a lack of association between H.?pylori and recurrent abdominal pain of childhood, gastroesophageal reflux disease, and growth retardation. Recent probiotic trials have not shown a benefit on H.?pylori eradication in children, while sequential therapy remains an attractive therapeutic eradication strategy in children, which requires validation in different geographic regions. 相似文献
107.
A Fenech P P Dendy J K Hussey B Bennett A S Douglas 《BMJ (Clinical research ed.)》1980,280(6231):1571-1573
Platelets from eight patients thought clinically to have deep venous thrombosis were labbelled with indium-111 and reinjected. Subsequent scanning of the patients with a wholebody scanner and imaging with a gammacamera showed focal accumulation of the label at five sites in four legs, which correlated precisely with the sites of venous thrombi identified by ascending venography. This technique is a useful addition to methods for diagnosis venous thrombosis. 相似文献
108.
109.
Rescaling the trophic structure of marine food webs 总被引:1,自引:0,他引:1
Nigel E. Hussey M. Aaron MacNeil Bailey C. McMeans Jill A. Olin Sheldon F.J. Dudley Geremy Cliff Sabine P. Wintner Sean T. Fennessy Aaron T. Fisk 《Ecology letters》2014,17(2):239-250
Measures of trophic position (TP) are critical for understanding food web interactions and human‐mediated ecosystem disturbance. Nitrogen stable isotopes (δ15N) provide a powerful tool to estimate TP but are limited by a pragmatic assumption that isotope discrimination is constant (change in δ15N between predator and prey, Δ15N = 3.4‰), resulting in an additive framework that omits known Δ15N variation. Through meta‐analysis, we determine narrowing discrimination from an empirical linear relationship between experimental Δ15N and δ15N values of prey consumed. The resulting scaled Δ15N framework estimated reliable TPs of zooplanktivores to tertiary piscivores congruent with known feeding relationships that radically alters the conventional structure of marine food webs. Apex predator TP estimates were markedly higher than currently assumed by whole‐ecosystem models, indicating perceived food webs have been truncated and species‐interactions over simplified. The scaled Δ15N framework will greatly improve the accuracy of trophic estimates widely used in ecosystem‐based management. 相似文献
110.
Pedro?A?Reche Derin?B?Keskin Rebecca?E?Hussey Petronela?Ancuta Dana?Gabuzda Ellis?L?ReinherzEmail author 《Medical immunology (London, England)》2006,5(1):1
Cytotoxic T lymphocytes (CTL) protect against viruses including HIV-1. To avoid viral escape mutants that thwart immunity, we chose 25 CTL epitopes defined in the context of natural infection with functional and/or structural constraints that maintain sequence conservation. By combining HLA binding predictions with knowledge concerning HLA allele frequencies, a metric estimating population protection coverage (PPC) was computed and epitope pools assembled. Strikingly, only a minority of immunocompetent HIV-1 infected individuals responds to pools with PPC >95%. In contrast, virus-naive individuals uniformly expand IFNγ producing cells and mount anti-HIV-1 cytolytic activity. This disparity suggests a vaccine design paradigm shift from infected to normal subjects. 相似文献